Another Irreverent Whine from Dr. Joe - Home Energy Pros2015-03-03T20:59:39Zhttp://homeenergypros.lbl.gov/forum/topics/another-irreverent-whine-from-dr-joe?commentId=6069565%3AComment%3A96098&xg_source=activity&feed=yes&xn_auth=noThismakes so much sense to me…tag:homeenergypros.lbl.gov,2012-10-22:6069565:Comment:970152012-10-22T14:59:01.188Ztedkiddhttp://homeenergypros.lbl.gov/profile/tedkidd
Thismakes so much sense to me. At some point delta t creates enough delta p to "break" or overcome the natural tendency of things to move toward equilibrium/mix and instead create/move toward stratification.
Thismakes so much sense to me. At some point delta t creates enough delta p to "break" or overcome the natural tendency of things to move toward equilibrium/mix and instead create/move toward stratification. No, the cellulose cap prevent…tag:homeenergypros.lbl.gov,2012-10-22:6069565:Comment:968192012-10-22T13:11:48.028ZRobert Riversonghttp://homeenergypros.lbl.gov/profile/RobertRiversong
<p>No, the cellulose cap prevents warm air from rising up ;-)</p>
<p>Oak Ridge National Lab ignored the silly debate about whether cold air falls or warm air rises and simply ascribed the loss of R-value to "convection" (which is both processes occurring simultaneously).</p>
<p>Whether loose-fill cellulose is a better air retarder than lay-in suspended ceiling tiles is anyone's guess, but fiberglass batts did not suffer from the R-value decline.</p>
<p>And what their testing showed is that the…</p>
<p>No, the cellulose cap prevents warm air from rising up ;-)</p>
<p>Oak Ridge National Lab ignored the silly debate about whether cold air falls or warm air rises and simply ascribed the loss of R-value to "convection" (which is both processes occurring simultaneously).</p>
<p>Whether loose-fill cellulose is a better air retarder than lay-in suspended ceiling tiles is anyone's guess, but fiberglass batts did not suffer from the R-value decline.</p>
<p>And what their testing showed is that the stack-effect convection that is not normally a problem in horizontal applications with low "head" can become so with very high delta-T.</p>
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<p></p>
<p align="center"><strong>Fixing Fiberglass Convection Problems with Loose-Fill Cellulose</strong></p>
<p align="center"><strong>Energy Design Update Volume 13, No.5; May 1993</strong></p>
<p> </p>
<p><em>Researchers at Oak Ridge National Laboratory are exploring ways to prevent or fix the problem of air convection in low-density loose-fill attic insulation.</em></p>
<p><em>Previous testing at Oak Ridge showed that low-density (0.5 pounds per cubic foot [lb/ft<sup>3</sup>]) loose-fill fiberglass suffers up to 50% loss of R-value at very cold attic temperature (-18°F) due to air convection within the insulation. However, laying fiberglass batts over the loose fill effectively stopped the convection problem. What if the low-density material was covered with higher-density loose fill instead of fiberglass batts?</em></p>
<p><em>To answer that question, Oak Ridge scientists tried blowing both cellulose and 0.7 lb/ft<sup>3</sup> fiberglass on top of low-density R-30 loose-fill fiberglass. The results were mixed: cellulose worked, fiberglass didn't.</em></p>
<p><em>When approximately two inches of cellulose (R-8) were added over the R-30 low-density fiberglass, the measured overall R-value remained at R-38 down to -18°F, indicating that the cellulose covering effectively prevented convection.</em></p>
<p><em>But the higher-density fiberglass apparently failed to stop convection at low temperatures. When an R-8 layer was added over the low-density material, it added R-8 to the overall R-value, but failed to restore the lost R-value due to convection.</em></p>
<p></p> Robert,
during heating season…tag:homeenergypros.lbl.gov,2012-10-22:6069565:Comment:971032012-10-22T11:47:16.645ZJohn Brookshttp://homeenergypros.lbl.gov/profile/JohnBrooks
<p>Robert,</p>
<p>during heating season....</p>
<p>Isn't the 2"-3" of cellulose that you mention acting like a continuous cap that retards the cold air from spilling into the 3-d network of voids(and displacing the warm air)?</p>
<p>and isn't your example a "better" air barrier than a lay-in suspended ceiling ?</p>
<p>Robert,</p>
<p>during heating season....</p>
<p>Isn't the 2"-3" of cellulose that you mention acting like a continuous cap that retards the cold air from spilling into the 3-d network of voids(and displacing the warm air)?</p>
<p>and isn't your example a "better" air barrier than a lay-in suspended ceiling ?</p> Early studies of (very) loose…tag:homeenergypros.lbl.gov,2012-10-18:6069565:Comment:964902012-10-18T16:24:50.928ZRobert Riversonghttp://homeenergypros.lbl.gov/profile/RobertRiversong
<p>Early studies of (very) loose-fill fiberglass in attics found enough vertical convection within the insulation to significantly undermine the insulating value of the fiberglass, but the same was not found with batts (except for poorly-installed batts with gaps), and as little as 2"-3" of cellulose on top of loose fill fiberglass was enough to virtually stop internal convection.</p>
<p>So it's really not much of an issue with modern materials and techniques in horizontal applications.</p>
<p>Early studies of (very) loose-fill fiberglass in attics found enough vertical convection within the insulation to significantly undermine the insulating value of the fiberglass, but the same was not found with batts (except for poorly-installed batts with gaps), and as little as 2"-3" of cellulose on top of loose fill fiberglass was enough to virtually stop internal convection.</p>
<p>So it's really not much of an issue with modern materials and techniques in horizontal applications.</p> The idea being the delta p ca…tag:homeenergypros.lbl.gov,2012-10-18:6069565:Comment:965812012-10-18T15:56:16.482Ztedkiddhttp://homeenergypros.lbl.gov/profile/tedkidd
<p>The idea being the delta p caused by 65-30 delta t would be enough to overcome the resistance of the batts? </p>
<p>Wouldn't it have a modulating/self-balancing effect? </p>
<p></p>
<p>In other words; if the point where delta p did NOT overcome the resistance was 30 delta t, wouldn't you expect that to be where equilibrium settled?</p>
<p>The idea being the delta p caused by 65-30 delta t would be enough to overcome the resistance of the batts? </p>
<p>Wouldn't it have a modulating/self-balancing effect? </p>
<p></p>
<p>In other words; if the point where delta p did NOT overcome the resistance was 30 delta t, wouldn't you expect that to be where equilibrium settled?</p> Of course, that's the picture…tag:homeenergypros.lbl.gov,2012-10-18:6069565:Comment:965732012-10-18T14:27:23.651ZRobert Riversonghttp://homeenergypros.lbl.gov/profile/RobertRiversong
<p>Of course, that's the picture of virtually all insulated attics. The delta-P across 12" of batts in your scenario is about 0.25 Pa. minus the resistance of the batts. The significant issues are air sealing at the ceiling (that's why we call it a "sealing"), and windwash through the batts if the sides of the "bathtub" are not well-sealed.</p>
<p>Dr. Joe's designs are always "perfect", so there's never any problems. ;-)</p>
<p></p>
<p>Of course, that's the picture of virtually all insulated attics. The delta-P across 12" of batts in your scenario is about 0.25 Pa. minus the resistance of the batts. The significant issues are air sealing at the ceiling (that's why we call it a "sealing"), and windwash through the batts if the sides of the "bathtub" are not well-sealed.</p>
<p>Dr. Joe's designs are always "perfect", so there's never any problems. ;-)</p>
<p></p> It seems to me that the attic…tag:homeenergypros.lbl.gov,2012-10-18:6069565:Comment:967532012-10-18T11:33:27.940ZJohn Brookshttp://homeenergypros.lbl.gov/profile/JohnBrooks
<p>It seems to me that the attic bathtub concept would not work so-well during the heating season...<br></br>In the same way that the crawlspace bathtub concept would not work so-well during the cooling season.…<a href="http://api.ning.com:80/files/4uLsgpBK3A*wBe*ehEYGJjleNiBrNlDOZ7m*p58BlQZJVusWxda39pptqt-DznZNLWudIKJFgOqV294lKJ8rPtPA-Rby9K50/tub2.png" target="_self"><img class="align-full" src="http://api.ning.com:80/files/4uLsgpBK3A*wBe*ehEYGJjleNiBrNlDOZ7m*p58BlQZJVusWxda39pptqt-DznZNLWudIKJFgOqV294lKJ8rPtPA-Rby9K50/tub2.png" width="529"></img></a></p>
<p>It seems to me that the attic bathtub concept would not work so-well during the heating season...<br/>In the same way that the crawlspace bathtub concept would not work so-well during the cooling season.<a href="http://api.ning.com:80/files/4uLsgpBK3A*wBe*ehEYGJjleNiBrNlDOZ7m*p58BlQZJVusWxda39pptqt-DznZNLWudIKJFgOqV294lKJ8rPtPA-Rby9K50/tub2.png" target="_self"><img class="align-full" src="http://api.ning.com:80/files/4uLsgpBK3A*wBe*ehEYGJjleNiBrNlDOZ7m*p58BlQZJVusWxda39pptqt-DznZNLWudIKJFgOqV294lKJ8rPtPA-Rby9K50/tub2.png" width="529"/></a></p> Nice Robert, I think you unco…tag:homeenergypros.lbl.gov,2012-10-15:6069565:Comment:967102012-10-15T17:31:40.784Ztedkiddhttp://homeenergypros.lbl.gov/profile/tedkidd
<p>Nice Robert, I think you uncovered a potential source of some confusion. </p>
<blockquote><p><span> there is no significant stack effect in shallow horizontal floor and ceiling spaces</span></p>
</blockquote>
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<p>Stack effect is not simply the height of the structure. It requires a connected air path from bottom to top. The weight of stack requires the whole column to build upon itself. If you have a 10 story building, but penetrations between floors are completely sealed you have…</p>
<p>Nice Robert, I think you uncovered a potential source of some confusion. </p>
<blockquote><p><span> there is no significant stack effect in shallow horizontal floor and ceiling spaces</span></p>
</blockquote>
<p></p>
<p>Stack effect is not simply the height of the structure. It requires a connected air path from bottom to top. The weight of stack requires the whole column to build upon itself. If you have a 10 story building, but penetrations between floors are completely sealed you have broken the column. You basically have 10 1 story boxes when it comes to stack pressure, not 1 10 story column. </p>
<p></p>
<p>What Joe appears to be saying is losses through porous insulation in unsealed cavities via increased convection are maybe not terribly significant. Just significant enough to improve comfort when designed thoughtfully. </p>
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<p>The big loss is from air flowing in and out of that space, carrying the btu's completely away to someplace else. Solve that leakage, and you can get creative in your placement of insulation. Make the floor comfortable and you keep humans away from thermostats. </p>
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<p>I can see how easy it might be to have this misunderstand of stack, make some attribution errors, and therefore see this suggested design as a complete departure from best practices. I guess this would not be something for building science 101 as it could lead to a fair amount of confusion. </p> I see what you're getting at…tag:homeenergypros.lbl.gov,2012-10-14:6069565:Comment:963982012-10-14T15:41:23.375ZRobert Riversonghttp://homeenergypros.lbl.gov/profile/RobertRiversong
<p>I see what you're getting at - that the cooled air under the slab would "fall" through the suspended ceiling and not be contained.</p>
<p>I think Joe's response, which he mentioned in the article, is that there is no significant stack effect in shallow horizontal floor and ceiling spaces, and all the delta-P is across the slab-as-air-barrier.</p>
<p>I do suspect, however, that there could be potential for condensation on the underside of the slab, depending on how cool that surface becomes…</p>
<p>I see what you're getting at - that the cooled air under the slab would "fall" through the suspended ceiling and not be contained.</p>
<p>I think Joe's response, which he mentioned in the article, is that there is no significant stack effect in shallow horizontal floor and ceiling spaces, and all the delta-P is across the slab-as-air-barrier.</p>
<p>I do suspect, however, that there could be potential for condensation on the underside of the slab, depending on how cool that surface becomes with the thermal lag of the concrete and what appears to be relatively little insulation below the floor.</p> Robert,
I was "wondering" if …tag:homeenergypros.lbl.gov,2012-10-14:6069565:Comment:963962012-10-14T12:37:25.076ZJohn Brookshttp://homeenergypros.lbl.gov/profile/JohnBrooks
<p>Robert,</p>
<p>I was "wondering" if the orientation of the "tub" might make a performance difference depending on the season.</p>
<p>The "tub" analogy reminded me of John Straube's Cylinders.(BSD-014)</p>
<p>In Straube's example...if he had not inverted the cylinder before bringing it back indoors... the cold air would have fallen down and out instead of being "contained".…</p>
<p>Robert,</p>
<p>I was "wondering" if the orientation of the "tub" might make a performance difference depending on the season.</p>
<p>The "tub" analogy reminded me of John Straube's Cylinders.(BSD-014)</p>
<p>In Straube's example...if he had not inverted the cylinder before bringing it back indoors... the cold air would have fallen down and out instead of being "contained".<a href="http://api.ning.com:80/files/aJFFlhA-gGWtbF6kexEkwjOhlB9OgWYCs5qHJ2U38k*G-gho4IGififxSwYbses0-BYllQAxAEF9xZE37W3qaI6JnPpsh6is/tubs.JPG" target="_self"><img class="align-full" src="http://api.ning.com:80/files/aJFFlhA-gGWtbF6kexEkwjOhlB9OgWYCs5qHJ2U38k*G-gho4IGififxSwYbses0-BYllQAxAEF9xZE37W3qaI6JnPpsh6is/tubs.JPG?width=721" width="721"/></a></p>